Conventional box springs for supporting mattresses are comprised of a lower wooden support frame and an upper wire mesh support grid which is secured to a steel frame. Between the upper grid and the lower wood frame there are disposed a plurality of springs which are generally helical or cylindrical coil springs. To insure that the axis of each of the springs remains vertical, each spring must be secured to both the upper grid and to the lower wood frame.
The prior art discloses a number of grid constructions which include means for securing the top or bottom coil of a spring to the grid. For example, U.S. Pat. No. 867,952 discloses a construction wherein the longitudinal grid wires are provided with ears or wings and the end coil of a spring is stretched around the ears. To insure that the coils of the spring remain stationary, so called tie rods are employed and are secured to the end coil of the spring by clips. One of the disadvantages of such a construction is the necessity of supplying such clips. Thus, from the point of view of the box spring manufacturer, the clips are another item of inventory and are another item which the spring assembler must have available and must mount on the product. As a result, both manufacturing and material costs are increased.
U.S. Pat. No. 3,199,122 discloses a construction which employs so called links to hold the springs on a grid. While such a construction probably functions adequately to hold the springs in place, several disadvantages attend the use and assembly of this construction. For example, when the support grid and the springs are assembled, each of the links must be essentially woven between the end coil of a spring and the wire mesh which comprises the support grid. Thus, assembly time and costs are increased and it is necessary for the assembler to have available not only a quantity of coil springs and a pair of grids but, additionally, a quantity of links. Further, after the assembly is completed and the mattress is used, the nature of the construction is such as to permit relative movement between the links and the end coils of the springs whereby noise may be generated.
Another prior art construction is disclosed in U.S. Pat. No. 3,662,411 wherein a wire mesh support grid is provided together with coil springs wherein the end coils of each spring are deformed so as to provide ears which may engage the support grid. Although this construction does not require the use of separately supplied links, it will be evident that conventional coil springs cannot be used, rather, each of the coil springs is modified so as to provide a plurality of ears in each end coil. As a result, the cost of the coil springs is increased and the commercial availability of acceptable springs may be reduced.
The present invention resides in a support grid construction which does not require the use of specially constructed springs. Additionally, a support grid embodying this invention will not require the use of separately mounted or woven connecting links. Thus, in accordance with this invention, a support grid may be supplied to a spring manufacturer and conventional coil springs may be mounted thereon without significantly extending the assembly time or requiring the use of additional parts. Moreover, the resulting box spring has been found to be particularly quiet, durable, stronger and provides a flatter surface with smaller openings for a mat to lie on when assembled.